This invention is generally directed to imaging members, and more specifically the present invention relates to the selection of certain polyurethanes which function as charge blocking layers for photoresponsive imaging members, especially seamless organic imaging members. In one embodiment, the present invention relates to an imaging member comprised of a supporting substrate, a conductive ground plane, a charge blocking layer comprised of a urethane polymer, an adhesive layer, a photogenerator, and a charge transport layer. Also, in another embodiment of the present invention, there are provided seamless imaging members comprised of a hole transport layer, a photogenerating layer, an adhesive layer, a hole blocking layer comprised of a urethane polymer, and a conductive supporting substrate. The aforementioned imaging members are useful in electrophotographic printing and imaging processes, and in particular, can be selected for the generation of latent images in electrostatic imaging systems. With further regard to the imaging members of the present invention, the primary function of the hole blocking layer is to prevent dark injection of charge carriers from the ground plane or conductive substrate into the photogenerating layer, thus significantly reducing the dark decay characteristics of imaging members.
Layered imaging members with blocking layers are known, especially those wherein the blocking layer is comprised of a metal oxide, or a siloxane, reference U.S. Pat. No. 4,464,450.
Illustrated in U.S. Pat. No. 4,562,132, the disclosure of which is totally incorporated herein by reference, entitled Photoresponsive Imaging Members Containing Electron Transport Overcoatings, are imaging members comprised of a supporting substrate, a hole transport layer comprised of an aryl amine hole transporting compound dispersed in an inactive resinous binder, a photogenerating layer comprised of a photogenerating pigment optionally dispersed in a resinous binder, and as a protective topcoating an electron transporting compound of the following formula dispersed in a resinous binder ##STR2## where X is cyano or alkoxycarbonyl groups, A and B are electron withdrawing groups, m is a number of from 0 to 2, n is the number 0 or 1, and W is an electron withdrawing group selected from the group consisting of acyl (COR), alkoxycarbonyl (COOR), alkylaminocarbonyl (CONHR), and derivatives thereof.
Moreover, illustrated in copending application U.S. Ser. No. 882,117, entitled Phoresponsive Imaging Members With Electron Transport Overcoatings, the disclosure of which is totally incorporated herein by reference, are inorganic photoresponsive imaging members having incorporated therein as protective overcoatings polycondensation polymers derived from the polycondensation of 2,2-bis(hydroxymethyl)-butyl 9-dicyanomethylene-fluorene-4-carboxylate, and diisocyanate. Also disclosed in the copending application are layered photoresponsive imaging members comprised of a supporting substrate, a photoconductive layer, an arylamine hole transport layer, and a protective overcoating layer comprised of the aforementioned polyurethane polymers. In addition, the polyurethane polymers of the copending application are useful as the top overcoating for positive-charging layered photoresponsive devices comprised of a supporting substrate, a hole transport layer, and a photoconductive layer, and wherein the polymers are of the following formula ##STR3## wherein A is a trivalent linkage; B is a functional group such as an ester (--OCO--), a carbonate (--OCOO--) or a carbamate (--OCONH--); R is a bivalent group, and n represents a certain number of repeating units.
The polyurethanes of the present invention are somewhat similar to the aforementioned polyurethane coatings. More specifically, the polyurethanes of the present invention contain therein certain highly flexible segments, thereby providing the desired flexibility characteristic useful for application in the belt-type imaging devices. Furthermore, the presence of the soft flexible segments in the polyurethanes of the present invention greatly improve their solubilities in common coating solvents such as aromatic hydrocarbons, tetrahydrofuran, chlorinated hydrocarbons, and the like, thereby enabling the coating process to be accomplished in a variety of solvents by different coating techniques, such as dip coating, spray coating, and the like. More importantly, the incorporation of the flexible segments into the polyurethane structure renders the synthesis of higher molecular-weight polyurethanes feasible, thus affording mechanically strong and highly durable polyurethane blocking layers. The polyurethanes of the present invention also display good adhesion properties, thereby improving the adhesion of the generator layer to the ground plane.
Also, in U.S. Pat. No. 4,820,601, the disclosure of which is totally incorporated herein by reference, there are illustrated imaging members with protective overcoatings comprised of the copolyurethanes selected as blocking layers for the same, or similar imaging members of the present invention.
There are disclosed in U.S. Pat No. 4,474,865 improved photoresponsive imaging members with electron transporting components containing specific dicyano fluoro ester moieties; U.S. Pat. No. 3,928,034, which illustrates the incorporation of electron transporting moieties chemically attached to polymers, reference columns 7 and 8; and U.S. Pat. Nos. 4,007,043; 4,063,947; 4,075,012; and 3,896,184. Also of interest are U.S. Pat. Nos. 3,108,092; 3,451,969; 4,063,947; and 4,203,764; and Holland Patent Publication No. 7606525. Of particular interest are U.S. Pat. No. 4,063,947 and Holland Patent Publication No. 7606525, which disclose imaging members with electron transport compounds, reference column 3, line 57, to column 4, line 30, of the '947 patent; U.S. Pat. Nos. 3,907,650, which discloses hole transport materials for an electron blocking layer reference column 3; U.S. Pat. No. 3,975,635, which discloses a xeroradiographic plate with a conductive backing member, an overlayer of selenium, and an intermediate layer of polyvinyl carbazole or an alloy of arsenic and selenium; U.S. Pat. No. 4,582,773 illustrating electrophotographic photoreceptors including a blocking layer formed from a doped microcrystalline semiconductor alloy; and U.S. Pat. Nos. 4,013,623; 4,050,934, which disclose a dicyanomethylene group as the electrical active moiety for use in electron transporting layer. Other patents of background interest are U.S. Pat. No. 4,465,751, which mentions cuprous iodide as a conductive substrate film; U.S. Pat. Nos. 2,901,348; 3,713,821; 3,879,199; 3,888,665; 3,891,435; 3,972,717; 4,010,031; 4,082,551; 4,106,935; 4,391,888; and 4,415,639.
While the above-described imaging members particularly those disclosed in the copending applications, and U.S. Pat No. 4,820,601, are suitable for their intended purposes, there continues to be a need for layered photoresponsive imaging members with functionally superior charge blocking layers. More specifically, there continues to be a need for charge blocking layers which can effectively block the dark injection of charge carriers from the ground plane into the photogenerating layer. Additionally, there continues to be a need for charge blocking layers with excellent flexibility characteristics, thereby enabling their use in belt-type organic imaging members. Furthermore, there is a need for organic charge blocking layer materials which are soluble in a variety of solvents thereby permitting improved coatability, and allowing economical spray and dip coating processes to be selected for the preparation thereof. Another need resides in the provision of charge blocking layers with acceptable desirable adhesive properties enabling the layer to adhere to the ground plane or conductive substrate, thereby improving the overall layered lamination integrity of the imaging members.